1. Field of the Invention
The present invention relates to a frame rate conversion processing apparatus that changes a frame rate of a first image signal to generate a second image signal, a frame rate conversion processing method, and a program.
2. Description of the Related Art
In the frame rate conversion for a video, it is conventionally feasible to prevent a converted video from becoming visually unnatural. For example, to perform the frame rate conversion, a conventional technique discussed in Japanese Patent Application Laid-Open No. 2003-069961 includes processing for generating predicted frame data based on a pre-conversion frame rate, a post-conversion frame rate, and a motion vector of the frame, inserting a predicted frame between frames of a pre-conversion video, and interpolating the motion of a subject to be captured in the video.
Further, there is an advanced imaging apparatus that can generate a higher frame rate video. However, if a video output apparatus represented by a television set cannot display a higher frame rate video, it is generally necessary to convert (reduce) the frame rate of an input video in advance so that the apparatus can display the input video.
In such a case, a video having been subjected to the frame rate conversion processing may become visually unnatural due to forcible reduction of the frame rate.
For example, there is an object that can be recognized as stably emitting light because temporal changes in luminance occur at a very high frequency and cannot be perceived by human eyes. If the frame rate of a video is changed, the above-described object may be recognized as temporally changing in luminance in a converted video.
FIGS. 16A and 16B illustrate an example of the frame rate conversion. An upper part of FIG. 16A illustrates temporal changes in luminance of fluorescent lighting in a case where the frequency of a power source is 50 Hz. The fluorescent lighting causes luminance changes at the frequency of 100 Hz, which is two times the frequency of the power source.
A lower part of FIG. 16A illustrates a row of frames that are successively arranged according to the order of image capturing processing performed at the rate of 300 frames per second. As apparent from the illustrated row of frames, the brightness of the fluorescent lighting periodically decreases (becomes dark) at intervals of 1/100 sec.
If the above-described row of frames is reproduced at 300 fps (i.e., 300 frames per second), the brightness of the fluorescent lighting causes luminance changes at the frequency of 100 Hz. However, it is generally known that the time frequency at which temporal changes in luminance cannot be visually recognized by human eyes is equal to or greater than 60 Hz. The light of fluorescent lighting recognized by human eyes is the light constantly maintaining predetermined brightness (hereinafter, referred to as “stable light”).
An example conversion of the frame rate from 300 Hz to 60 Hz is described below with reference to the lower part of FIG. 16A and FIG. 16B, according to which a new row of frames can be generated by successively extracting one frame at intervals of 1/60 sec from the above-described row of frames.
More specifically, the lower part of FIG. 16A illustrates a row of frames that is not yet subjected to the frame rate conversion processing. FIG. 16B illustrates a row of frames obtained through the frame rate conversion processing. When the row of frames illustrated in the FIG. 16B is reproduced at 60 fps, the luminance of the fluorescent lighting in a reproduced video changes at the frequency of 20 Hz as illustrated in FIG. 16B. More specifically, the temporal changes in luminance occur at intervals of 1/20 sec and therefore the changes in luminance of the fluorescent lighting can be perceived by human eyes.
Therefore, even when the above-described conventional technique is employed to generate a predicted frame that interpolates a motion and insert the generated predicted frame between frames, an object to be visually recognized as stable light may be erroneously recognized as temporally changing in luminance in a frame rate converted video, as described above.